Vibrating belt powder cloud generator for xerography



July 7, 1964 w. c. YORK VIBRATING BELT POWDER CLOUD GENERATOR FORXEROGRAPHY Filed April 28, 1961 Fig.

WILL/AM C YORK WMM ATTORNE Y 5 United States Patent Ofifice 3,140,199Patented July 7, 1964 3,140,199 VIBRATIN G BELT POWDER CLOUD GENERATORFOR XEROGRAPHY William C. York, Rochester, N.Y., assignor to EastmanKodak Company, Rochester, N.Y., a corporation of New Jersey Filed Apr.28, 1961, Ser. No. 106,202 7 Ciaims. (Cl. 118-637) This inventionrelates to Xerographic developing equipment and particularly toapparatus for applying xerographic toner to an irnagewiseelectrostatically charged surface.

Many systems and types of apparatus have been developed for applyingtoner to electrostatic images on the surfaces of photoconductors whichhave been exposed to light. There is in all of these the problem ofproducing uniformity of development, adequate density in the chargedareas, zero density in the background or uncharged areas and freedomfrom dust and dirt.

The object of the present invention is to overcome all suchdifiiculties. Triboelectric toner powders are commonly used inxerographic processes since they become charged merely by agitation orrubbing and this charge is utilized in the toning or developing step.The present invention utilizes the triboelectric charge for two otherpurposes. The present invention employs a belt conveyor and thetriboelectricity is used to make the powder adhere to the belt uniformlyfor conveyance to the developing station. Secondly this triboelectriccharge creates an adherence of the toner to the belt which must beovercome (primarily by agitation as discussed below) if the fieldcreated by the imagewise charge on the photoconductive surface is to beeffective in forming an image. These opposing effects insure uniformityso that toner does not tend to transfer to the background area of theimage.

However, this triboelectric adherence of the toner to the belt mightintroduce non-uniformity since some toner particles would be in directcontact with the belt and others would be spaced slightly therefrom. Anylack of uniformity thus created is overcome, according to the presentinvention by mechanical vibration or agitation of the belt right at thedeveloping station. This mechanical agitation may be provided by rollerscontacting the back of the belt, where such rollers are caused tovibrate rapidly by a high speed rotating cam. A horn emitting sound orultrasonics impinging against the back of the belt constitute anotherform of belt vibrator. In preferred embodiments of the invention thebelt contains a ferromagnetic material such as a layer of iron or mayconsist of iron. In this case the vibration is provided simply by anelectromagnet connected to an AC. source.

The belt with the toner powder may pass through the developing andvibrating station at any angle such as horizontally or preferablyvertically. The toner is applied to the belt by a system including oneor more brushes and means for agitating or stirring the toner powder inthe supply bin. The brush itself may act as the toner agitating means orthe toner may be kicked up by one member such as a rotating helix andtransferred to a brush which in turn transfers it to the belt so thatthe toner on the belt is fully triboelectrically charged and held to thebelt solely by this charge. Brushes and rotating helices for applicationof toner particles from a bin to a surface are known.

Two special modifications of the toner applicator warrant mentionalthough they are not essential to the present invention. In one case afriable cake of toner is ground or scrubbed by an abrasive drum whichgrinds off toner particles and applies them to the conveyor belt. In theother case, the conveyor belt itself is abrasive and grinds off thetoner from the friable cake and carries it to the developing station.Either system works well with the conveyor belt required by the presentinvention.

The essential feature of the invention is the mechanical vibration ofthe belt at the developing station, sufficient to overcome thetriboelectric attraction between the toner and the belt. It should benoted that the toner is moved to the developing station without the useof air pressure, which is one of the commonest causes of dust, since theair pressure tends to spread toner unduly throughout any developingmachine. Other advantages and the principle of the invention will befully understood from the following description when read in connectionwith the accompanying drawing in which:

FIG. 1 schematically illustrates one preferred embodiment of theinvention.

FIG. 2 similarly illustrates another preferred embodiment of theinvention.

FIG. 3 illustrates an alternative form of mechanical vibration and,

FIG. 4 illustrates a preferred form of toner applicator.

In FIG. 1 a xerographic sheet 10 which has been charged and exposed soas to have an electrostatic image on the surface thereof is held bymeans (not shown) against a metal plate 11. A belt 15 of metal orplastic is moved by rotating drums 16 and 17 immediately below thexerographic sheet 10 and carries toner particles 24 to the developingstation at which the sheet 10 is located. The choice between metal andplastic affects the type of development. So called solid areadevelopment without edge effects occurs when the belt is conducting oris insulating and backed by a conductor. Fringe development (morepronounced at the edges of image areas) occurs when the belt isinsulating and not backed by a conductor.

The toner is applied from a bin 21 containing loose particles 22 oftoner, by means of a rotating brush 23 to the surface of the belt 15which moves above the brush 23. The brush 23 tends to stir the powder 22so as to create triboelectric charges and due to these charges only, thepowder adheres to the belt 15. Two devices are here used to insuretransfer of the toner particles 24 to the charged area of the image 10.One of these is an electrostatic bias between the belt and the backingplate 11, which bias is provided by a source of potential indicatedschematically at 18. This first feature is optional and the bias whenused may be of either polarity depending upon the toner polarity andupon whether the toner is to be deposited in the charged or unchargedareas of electrostatic image. The triboelectric adherence of the powderto the belt 15 is overcome or reduced to a small uniform amount ofattraction by means of transverse rods or rollers 26 contacting the backof the belt 15 at the development station. These rollers 26 aresupported at their edges by a mount 27 which moves rapidly up and downby the operation of a cam 28 which is rotated rapidly by means of amotor (not shown). This simple mechanism gives excellent prints withclean highlights and with a minimum of dust and smoke.

The slightly more sophisticated apparatus shown in FIG. 2 has been foundto give even greater uniformity with a minimum of variations and aminimum of maintenance difiiculties over long periods of time. In thearrangement shown in FIG. 2 the belt 15 is of fairly stifi but stillflexible sheet iron. The vibration at the toning station is providedsimply by an electromagnet 30 powered from an AC. source indicatedschematically at 31. This causes the belt to vibrate and reduce orovercome the triboelectric attraction of the powder to the belt. Auniformly controlled amount of powder transfers to the desired areas ofthe xerographic sheet 10. In this FIG. 2, the toner particles 32 areagitated by relatively soft brushes 33 which rotate deep into the tonerparticles and carry toner to the bottom of the belt 15. The container 34for the toner consists of two, more or less cylindrical, sections shapedto insure a high degree of agitation of the toner as the brushes arerotated. The'distance of the brushes 33 from the belt 15 is adjusted togive the desired thickness of toner particles on the belt 15.

FIG. 3 schematically illustrates the use of a mechani cally operatedhorn 40 driven by a motor not shown, which horn causes fairly intensesound waves to impinge across the back of the belt 15 at the toningstation. Actually all of the forms of the invention tend to create somesound and it is preferable to have some sound insulation in the housingof the machine, but the intensity of the sound need not be very high andthe 60 cycle hum produced by the arrangement shown in FIG. 2, for example, is not objectionable. Even lower frequencies are employed in thearrangement shown in FIG. 1 so that the only audible sound is the noiseset up by the mechanical moving parts rather than the intendedfrequencies of this motion itself.

In FIG. 4 the bin of toner particles 45 is'cylindrically shaped withextended sides to catch any falling toner particles. The toner in thebin is continuously agitated by rotating a helix or spring shaped member47 about its axis 48. Sometimes the helical member is made with areverse pitch at the center and is turned so that the toner tends to bedriven from the ends to the center of the cylindrical bin. This metalhelix 47 does pick up some particles primarily by the triboelectriccharge and these particles are transferred by rotating brushes 50 to thesurface of the belt 15. The two stages of application of the toner eachof which requires triboelectric charge, insures that the particlesapplied to the belt 15 and hence conveyed to the toner station are onlythose so charged.

Having thus described various preferred embodiments of my invention Iwish to point out that it is not limited thereto but includesmodifications thereof within the scope of the appended claims.

I claim:

1. In a xerographic developing machine, a toner applicator comprisingmeans for supporting an electros'tatically charged layer to bedeveloped, a flat belt with a section thereof in an area close to andparallel to said layer when so supported, means remote from said areafor triboelectrically loading said belt with toner powder, means formoving said belt for carrying triboelectrically, held toner powder tosaid area close to said layer and means positioned adjacent to said areaand on the opposite side of saidbelt from said layer for vibrating saidsection of said belt in said area.

2. An applicator according to claim 1 in which said belt is metal. 7

3. An applicator according to claim 1 in which said electrostaticallycharged layer is supported in a substantially vertical plane.

, 4. An applicator according to claim 1 in which the means fortriboelectrically loading said belt consists of a bin of toner powder,means for agitating the powder in said bin and brushes transferringtoner powder from the bin to the belt.

5. An applicator according to claim 1 in which said belt contains ironand in which said vibrating means includes A.C. operated electromagnets.

6. An applicator according to claim 1 in which said vibrating meansconsists of a source of sound for impinging sound waves on the side ofsaid belt away from said electrostatically charged layer.

7. An applicator according to claim 1 in which said vibrating meansconsists of mechanically vibrating rods contacting the surface of saidbelt facing away from said electrostatically charged layer.

References Cited in the file of this patent UNITED STATES PATENTS2,276,328 Melton et al. Mar. 17, 1942 2,376,343 Carlton May 22, 19452,748,746 Wommelsdorf June 5, 1956 2,829,025 Clemens et al. Apr. 1, 19582,895,847 Mayo- July 21, 1959 2,901,374 Gundlach a Aug. 25, 19592,902,974 Greaves Sept. 8, 1959 2,910,963 Herman Nov. 3, 1959 3,013,890Bixby Dec. 19, 1961

1. IN A XEROGRAPHIC DEVELOPING MACHINE, A TONER APPLICATOR COMPRISINGMEANS FOR SUPPORTING AN ELECTROSTATICALLY CHARGED LAYER TO BE DEVELOPED,A FLAT BELT WITH A SECTION THEREOF IN AN AREA CLOSE TO AND PARALLEL TOSAID LAYER WHEN SO SUPPORTED; MEANS REMOTE FROM SAID AREA FORTRIBOELECTRICALLY LOADING SAID BELT WITH TONER POWDER, MEANS FOR MOVINGSAID BELT FOR CARRYING TRIBOELECTRICALLY HELD TONER POWDER TO SAID AREACLOSE TO SAID LAYER AND MEANS POSITIONED ADJACENT TO SAID AREA AND ONTHE OPPOSITE SIDE OF SAID BELT FROM SAID LAYER FOR VIBRATING SAIDSECTION OF SAID BELT IN SAID AREA.